Chimpanzees with enzymatic and histologic evidence of chronic NANB hepatitis will be treated with adenine arabinoside. Serial liver function studies and liver biopsy material will be obtained for 6-12 months after treatment in an attempt to assess the effect of treatment of the chronic hepatitis per se. In addition, post-treatment serums will be inoculated into additional chimpanzees to assess infectivity in comparison with pre-treatment serums. It is possible that treatment will ameliorate infectivity without altering hepatic inflammatory disease.